Gas hydrate is one of the most potential unconventional and clean alternative energy sources besides shale gas, coal seam and dense gas. It is mainly an ice-like “clathrate compound” formed by methane or other small gas molecular (such as ethane, propane and carbon dioxide) and water molecular at high pressure and low temperature. Exploitation and utilization of gas hydrate to alleviate energy shortage pressure and structural adjustment of energy is significant. But how to be long-term, steady, safe and efficient exploitation of gas hydrate has been a difficult problem in academic and engineering fields. The mechanical stability of gas hydrate formation and well wall in the process of exploitation is related to the success or failure of the hydrate development project. In China's shenhu sea, the gas hydrate is mainly distributed in fine-grained sediment. The size of mineral particles is in a range from about 8 to 63 μm, and the clay content is high, so the mechanical behavior of gas hydrate and mineral particle is studied at pore scale. In particular, the adhesion force between gas hydrate and mineral particles is very important to reveal the characteristics of friction, cohesion and relative movement between gas hydrate and mineral particles, and to evaluate the reservoir, the wellbore mechanical stability.
With an atomic force microscope (AFM), the force-displacement curve has been widely used in the measurement of adhesion force of micro-particles. The micro-particles are adhered to the AFM probe. By changing the voltage of the piezo scanner of AFM, the micro-particles on the probe can move up and down from micron to nano-scale on the sample surface. When the micro-particles are close to the sample to a certain extent, the micro-particles will adhere to the sample surfaces. Once the micro-particles and sample surfaces are in contact, the probe cantilever will deflect. The deflection was measured by optical method and the deflection signal was recorded. The force between micro-particles and sample surfaces is the deflection multiplied by the spring constant and sensitivity of the probe. The relationship between force and position of piezo scanner is called force-displacement curve. Then the micro-particles move upward and pull off from sample surfaces. The force that separates the micro-particles from the surface of the sample is the adhesion force. Generally, AFM can only be tested at atmospheric pressure, and its detection laser will heat the probe. When temperature of the probe is higher than the gas hydrate phase equilibrium temperature, it will induce gas hydrates phase transition. Therefore, how to maintain the gas hydrate sample stability in the process of testing is the key problem of the technique applying to gas hydrate testing. In order to introduce the technique of force-displacement curve into the field of testing the mechanical behavior between gas hydrate and mineral particles. The present invention provides a solution to how to maintain the gas hydrate sample stability and reduce the AFM probe temperature.
Therefore, there is room for improvement within the art.